The present invention relates to an apparatus for applying high-frequency electromagnetic energy, such as microwave energy, to a material and methods for tuning such an apparatus. More specifically, the invention relates to a microwave apparatus configured to apply microwave energy to a continuously moving web, and a method for tuning the microwave apparatus.
Apparatus that are designed to apply high frequency electromagnetic energy, such as microwave energy, to materials are known in the art. It is generally advantageous to be able to tune these apparatus such that they may be used to more efficiently process the materials without damaging or burning the material. Generally microwave apparatus are tuned by adjusting appointed tuning components in a conventional, iterative manner to maximize the energy absorbed into the load (i.e., the target material), and to minimize the reflected energy. Accordingly, the tuning components (such as an aperture plate or stub tuner) can be systematically varied to maximize the energy absorbed into the load and minimize the reflected energy.
Nonetheless, tuning of the microwave apparatus can become more challenging in industrial settings where it may be desirable to have a high-speed converting process continuously pass materials through such an apparatus. In such a situation, changes to the material passing through the apparatus can make it desirable or necessary to regularly tune the apparatus to accommodate these changes, especially if the material is prone to burn or combust. Accordingly, certain methods and apparatus have been developed to tune microwave devices that are suitable for such industrial settings.
Unfortunately, in certain circumstances, such methods and apparatus have not been completely satisfactory. For example, one way of tuning the apparatus is to change the volume inside the chamber where the material is exposed to energy. However, these methods typically employ components of the apparatus being in moving contact with each other. This approach in many instances can lead to gapping between the moving components which in turn can undesirably lead to arcing within the chamber. Such arcing can cause the target material to scorch or combust. Moreover, depending on the arrangement of the moving components, the movement of the components of the microwave apparatus can undesirably shift the focus of the energy field from the path of the material through the apparatus.
Thus, there is a need for a microwave apparatus and method that does not rely on components of the apparatus being in moving contact with each other. Further, there is a need for a microwave method and apparatus that provides for the tuning of the apparatus while maintaining the energy field focused on the target material.